Surface acoustic wave device incorporating single crystal LiNbO3

ABSTRACT

A surface acoustic wave device includes at least diamond, a single crystal LiNbO 3  layer formed on the diamond, and an interdigital transducer formed in contact with the LiNbO 3  layer and uses a surface acoustic wave (wavelength: λ n  μm) in an nth-order mode (n=1 or 2). When the thickness of the LiNbO 3  layer is t 1  (μm), kh 1  =2π(t 1  /λ n ) and the cut orientation (θ, Φ, and ψ represented by an Eulerian angle representation) with respect to the crystallographic fundamental coordinate system of the LiNbO 3  layer are selected from values within specific ranges. Consequently, a surface acoustic wave device which increases the propagation velocity (V) of a surface acoustic wave and improves the electromechanical coupling coefficient (K 2 ) is realized.

RELATED APPLICATIONS

This is a Continuation-In-Part application of application Ser. No.08/790,524 filed on Jan. 29, 1997, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave device whichimproves the propagation velocity (V) and the electromechanical couplingcoefficient (K²) of a surface acoustic wave.

2. Related Background Art

Surface acoustic wave devices using a surface acoustic wave (to bereferred to as an "SAW" hereinafter) propagating on a solid surface havethe following characteristic features which are common toelectromechanical functional parts.

1) Compact and lightweight.

2) Excellent in vibration resistance and high-impact properties.

3) Highly reliable because of few product variations.

4) Since the circuits need no adjustment, the mounting process can beeasily automated and simplified.

In addition to the above characteristic features common toelectromechanical functional parts, the SAW devices also have variousadvantages such as a relatively good temperature stability, a longservice life, and excellent phase characteristics. For this reason, theSAW devices can be popularly used as frequency filters, resonators,delay devices, signal processing devices, convolvers, opto-electronicfunctional devices, and the like.

As is known, for such SAW devices, a multilayer structure with an LiNbO₃layer formed on diamond is used, paying attention to the fact thatLiNbO₃ is chemically stabler (acid resistance and alkali resistance)than, e.g., ZnO.

For application as a frequency filter, an electromechanical couplingcoefficient (K²) used as an index of conversion efficiency from anelectrical energy to a mechanical energy is about 0.15% to 0.7% for anarrowband filter, about 0.7% to 3% for an intermediate-band filter, or3% to 10% for a wideband filter.

In the field of the above-described SAW devices, along with a recenttendency in multichannel or higher-frequency arrangements in the fieldof communications including satellite communication and mobilecommunication, the development of devices usable in a higher frequencyrange (e.g., GHz band) has been desired.

An operating frequency f of an SAW device is generally determined byf=V/λ (V is the propagation velocity of an SAW, and λ is the wavelengthof the SAW). The wavelength λ depends on the period of an interdigitaltransducer, as will be described later. However, the wavelength λ of anSAW to be used for the device can hardly be extremely shortened becauseof the limitation in micropatterning technique such as photolithography.Therefore, to raise the operating frequency of the SAW device, it ispreferable to increase the propagation velocity V of the SAW.

In the above-described field of communications represented by satellitecommunication and mobile communication, further power saving and sizereduction of an entire device are required mainly from the viewpoint ofmounting of the SAW device. In addition to the above-described higherfrequency, an improvement in the electromechanical coupling coefficient(K²) as the index of conversion efficiency from an electrical energy toa mechanical energy is required.

In recent years, therefore, for SAW devices to be widely used, a strongdemand for not only an increase in propagation velocity V of an SAW tobe used for the devices (e.g., V≧7,000 m/s) but also an increase inelectromechanical coupling coefficient (K²) (e.g., K² ≧2%) has arisen.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an SAW device whichincreases the propagation velocity V of an SAW and improves theelectromechanical coupling coefficient (K₂) of the SAW.

As a result of extensive studies, the present inventors found thefollowing fact. In an SAW device having a structure with single crystalLiNbO₃ and diamond layers and an interdigital transducer, the aboveobject can be achieved, i.e., an SAW device which increases thepropagation velocity V of an SAW and improves the electric-mechanicalcoupling coefficient (K²) of the SAW can be realized by combining thecrystal orientation in the single crystal LiNbO₃ layer and a parameterkh₁ =2π(t₁ /λ) (λ: the wavelength [μm] of an SAW to be used, t₁ : thethickness [μm] of the LiNbO₃ layer) and adjusting this combination.

More specifically, according to the present invention, there is provideda surface acoustic wave device comprising diamond, a single crystalLiNbO₃ layer formed on a surface of the diamond, and an interdigitaltransducer formed on one of a surface of the LiNbO3 layer and aninterface between the diamond and the LiNbO₃ layer, wherein a crystalorientation of the LiNbO₃ layer with respect to an exposed surface ofthe LiNbO₃ layer and a propagation direction of an SAW (cut orientationwith respect to the crystallographic fundamental coordinate system ofthe LiNbO₃ layer), and a ratio of a thickness of the LiNbO₃ layer to awavelength of the SAW to be used are selected such that a velocity V ofthe SAW to be used becomes 8,000 m/s and an electromechanical couplingcoefficient K² becomes 10% or more.

Therefore, an SAW device having characteristics representing asatisfactory propagation velocity V (≧8,000 m/s) and a satisfactoryelectromechanical coupling coefficient K² (≧10%) is realized.

In the SAW device of the present invention, preferably, the diamond is adiamond layer formed on a base material, and when a thickness of thediamond layer is t₂ [μm], the wavelength of the SAW to be used is λ, andkh₂ =2π(t₂ /λ), the following relation is satisfied:

kh₂ ≧4

If the diamond layer is thin, the SAW characteristics vary. However,when the thickness t₂ [μm] of the diamond layer is set such that kh₂ ≧4holds, the variation amount poses no practical problem. In addition,according to the finding of the present inventors, kh₂ ≧8 is morepreferable. With this arrangement, the variation amount can be furtherdecreased.

The present invention will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings, which aregiven by way of illustration only and are not to be considered aslimiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will beapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of an Eulerian angle representation;

FIG. 2 is a sectional view showing the structure of an SAW deviceaccording to the first embodiment of the present invention;

FIG. 3 is an explanatory view of the shape of the first example (singleelectrode) of an interdigital transducer;

FIG. 4 is an explanatory view of the shape of the second example (doubleelectrode) of the interdigital transducer;

FIG. 5 is a graph showing the relationship between kh₁ and a propagationvelocity V of an SAW in the 1st-order mode;

FIG. 6 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.2, Φ=0°);

FIG. 7 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.2, Φ=10°);

FIG. 8 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.2, Φ=20°);

FIG. 9 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.2, Φ=30°);

FIG. 10 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.325, Φ=0°);

FIG. 11 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.325, Φ=10°);

FIG. 12 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.325, Φ=20°);

FIG. 13 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.325, Φ=30°);

FIG. 14 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.45, Φ=0°);

FIG. 15 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.45, Φ=10°);

FIG. 16 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.45, Φ=20°);

FIG. 17 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.45, Φ=30°);

FIG. 18 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.7, Φ=0°);

FIG. 19 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.7, Φ=10°);

FIG. 20 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.7, Φ=20°);

FIG. 21 is a graph showing the evaluation result of K² in the firstembodiment (kh₁ =0.7, Φ=30°);

FIG. 22 is a sectional view showing the structure of an SAW deviceaccording to the second embodiment of the present invention;

FIG. 23 is a graph showing the relationship between kh₁ and apropagation velocity V of an SAW in the 2nd-order mode;

FIG. 24 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =0.6, Φ=0°);

FIG. 25 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =0.6, Φ=10°);

FIG. 26 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =0.6, Φ=20°);

FIG. 27 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =0.6, Φ=30°);

FIG. 28 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =0.85, Φ=0°);

FIG. 29 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =0.85, Φ=10°);

FIG. 30 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =0.85, Φ=20°);

FIG. 31 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =0.85, Φ=30°);

FIG. 32 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =1.1, Φ=0°);

FIG. 33 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =1.1, Φ=10°);

FIG. 34 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =1.1, Φ=20°);

FIG. 35 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =1.1, Φ=30°);

FIG. 36 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =1.6, Φ=0°);

FIG. 37 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =1.6, Φ=10°);

FIG. 38 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =1.6, Φ=20°);

FIG. 39 is a graph showing the evaluation result of K² in the secondembodiment (kh₁ =1.6, Φ=30°);

FIG. 40 is a sectional view showing the structure of an SAW deviceaccording to the third embodiment of the present invention;

FIG. 41 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.2, Φ=0°);

FIG. 42 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.2, 101 =10°);

FIG. 43 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.2, Φ=20°);

FIG. 44 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.2, Φ=30°);

FIG. 45 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.325, Φ=0°);

FIG. 46 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.325, Φ=10°);

FIG. 47 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.325, Φ=20°);

FIG. 48 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.325, Φ=30°);

FIG. 49 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.45, Φ=0°);

FIG. 50 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.45, Φ=10°);

FIG. 51 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.45, Φ=20°);

FIG. 52 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.45, Φ=30°);

FIG. 53 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.7, Φ=0°);

FIG. 54 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.7, Φ=10°);

FIG. 55 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.7, Φ=20°);

FIG. 56 is a graph showing the evaluation result of K² in the thirdembodiment (kh₁ =0.7, Φ=30°);

FIG. 57 is a sectional view showing the structure of an SAW deviceaccording to the fourth embodiment of the present invention;

FIG. 58 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =0.6, Φ=0°);

FIG. 59 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =0.6, Φ=10°);

FIG. 60 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =0.6, Φ=20°);

FIG. 61 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =0.6, Φ=30°);

FIG. 62 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =0.85, Φ=0°);

FIG. 63 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =0.85, Φ=10°);

FIG. 64 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =0.85, Φ=20°);

FIG. 65 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =0.85, Φ=30°);

FIG. 66 is a graph showing the evaluation result of K² 'in the fourthembodiment (kh₁ =1.1, Φ=0°);

FIG. 67 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =1.1, Φ=10°);

FIG. 68 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =1.1, Φ=20°);

FIG. 69 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =1.1, Φ=30°);

FIG. 70 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =1.6, Φ=0°);

FIG. 71 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =1.6, Φ=10°);

FIG. 72 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =1.6, Φ=20°);

FIG. 73 is a graph showing the evaluation result of K² in the fourthembodiment (kh₁ =1.6, Φ=30°);

FIG. 74 is a sectional view showing the structure of an SAW deviceaccording to the fifth embodiment of the present invention;

FIG. 75 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.2, Φ=0°);

FIG. 76 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.2, Φ=10°);

FIG. 77 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.2, Φ=20°);

FIG. 78 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.2, Φ=30°);

FIG. 79 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.325, Φ=0°);

FIG. 80 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.325, Φ=10°);

FIG. 81 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.325, Φ=20°);

FIG. 82 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.325, Φ=30°);

FIG. 83 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.45, Φ=0°);

FIG. 84 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.45, Φ=10°);

FIG. 85 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.45, Φ=20°);

FIG. 86 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.45, Φ=30°);

FIG. 87 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.7, Φ=0°);

FIG. 88 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.7, Φ=10°);

FIG. 89 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.7, Φ=20°);

FIG. 90 is a graph showing the evaluation result of K² in the fifthembodiment (kh₁ =0.7, Φ=30°);

FIG. 91 is a sectional view showing the structure of an SAW deviceaccording to the sixth embodiment of the present invention;

FIG. 92 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =0.6, Φ=0°);

FIG. 93 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =0.6, Φ=10°);

FIG. 94 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =0.6, Φ=20°);

FIG. 95 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =0.6, Φ=30°);

FIG. 96 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =0.85, Φ=0°);

FIG. 97 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =0.85, Φ=10°);

FIG. 98 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =0.85, Φ=20°);

FIG. 99 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =0.85, Φ=30°);

FIG. 100 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =1.1, Φ=0°);

FIG. 101 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =1.1, Φ=10°);

FIG. 102 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =1.1, Φ=20°);

FIG. 103 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =1.1, Φ=30°);

FIG. 104 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =1.6, Φ=0°);

FIG. 105 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =1.6, Φ=10°);

FIG. 106 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =1.6, Φ=20°);

FIG. 107 is a graph showing the evaluation result of K² in the sixthembodiment (kh₁ =1.6, Φ=30°);

FIG. 108 is a sectional view showing the structure of an SAW deviceaccording to the seventh embodiment of the present invention;

FIG. 109 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =0.6, Φ=0°);

FIG. 110 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =0.6, Φ=10°);

FIG. 111 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =0.6, Φ=20°);

FIG. 112 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =0.6, Φ=30°);

FIG. 113 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =0.85, Φ=0°);

FIG. 114 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =0.85, Φ=10°);

FIG. 115 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =0.85, Φ=20°);

FIG. 116 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =0.85, Φ=30°);

FIG. 117 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =1.1, Φ=0°);

FIG. 118 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =1.1, Φ=10°);

FIG. 119 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =1.1, Φ=20°);

FIG. 120 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =1.1, Φ=30°);

FIG. 121 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =1.6, Φ=0°);

FIG. 122 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =1.6, Φ=10°);

FIG. 123 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =1.6, Φ=20°);

FIG. 124 is a graph showing the evaluation result of K² in the seventhembodiment (kh₁ =1.6, Φ=30°);

FIG. 125 is a graph showing the evaluation result of K² in an evaluationexample (kh₁ =0.2, Φ=0°);

FIG. 126 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.2, Φ=10°);

FIG. 127 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.2, Φ=20°);

FIG. 128 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.2, Φ=30°);

FIG. 129 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.325, Φ=0°);

FIG. 130 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.325, Φ=10°);

FIG. 131 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.325, Φ=20°);

FIG. 132 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.325, Φ=30°);

FIG. 133 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.45, Φ=0°);

FIG. 134 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.45, Φ=10°);

FIG. 135 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.45, Φ=20°);

FIG. 136 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.45, Φ=30°);

FIG. 137 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.7, Φ=0°);

FIG. 138 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.7, Φ=10°);

FIG. 139 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.7, Φ=20°); and

FIG. 140 is a graph showing the evaluation result of K² in theevaluation example (kh₁ =0.7, Φ=30°).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, a single crystal LiNbO₃ layer is used. Asshown in FIG. 1, the crystal orientation of the LiNbO₃ layer isrepresented by an Eulerian angle representation (θ,Φ,ψ)on an orthogonalcoordinate system (X,Y,Z) in which the Z-axis is set along the normaldirection of the cut plane, and the X-axis is set along the SAWpropagation direction (one direction on the cut plane of the LiNbO₃layer, which is determined by the shape of an interdigital transducer)when viewed from the LiNbO₃ crystallographic fundamental coordinatesystem (x,y,z) of the LiNbO₃ layer.

The LiNbO₃ crystal has a three-time mirror surface symmetry (3 m). Forthis reason, (i) the characteristics of the LiNbO₃ layer at θ of 0° to180° match those at θ of 180° to 360°, (ii) the characteristics of theLiNbO₃ layer at ψ of 0° to 180° match those at ψ of 180° to 360°. Inaddition, (iii) the characteristics of the LiNbO₃ layer at Φ of 0° to120° match those at Φ of 120° to 240° and 240° to 360°. As an additionalplus, (iv) the characteristics of the LiNbO₃ layer at Φ of 0° to 30°, θof 0° to 180°, and ψ of 0° to 180° match those at ψ of 60° to 30°, θ of180° to 0°, and ψ of 180° to 0°, and (v) the characteristics of theLiNbO₃ layer at Φ of 0° to 60°, θ of 0° to 180°, and ψ of 0° to 180°match those at Φ of 60° to 120°, θ of 180° to 0°, and ψ of 180° to 0°.This means the characteristics of the LiNbO₃ changes periodically everyΦ of 30°. So the embodiments described as follows are represented onlywithin 0°≦Φ≦30°, 0°≦θ≦180°, and 0°≦ψ≦180°. The characteristics inremaining region is determined from that in this region by thissymmetiry. Y. Shimizu et. al disclosed this LiNbO₃ characteristics in"Characteristics of Leaky Surface Acoustic Waves on LiNbO₃ and the NewCut", Japan Telecommunications Society Journal, Vol.J69-C No. 10,October 1986, pp. 1309-1314.

The embodiments of an SAW device of the present invention will bedescribed below with reference to the accompanying drawings. The samereference numerals denote the same elements throughout the drawings, anda detailed description thereof will be omitted.

(First Embodiment)

FIG. 2 is a sectional view showing the structure of an SAW deviceaccording to the first embodiment of the present invention. As shown inFIG. 2, the SAW device of the first embodiment comprises (a) diamond100, (b) a short-circuit electrode 200 formed on the diamond 100, (c) asingle crystal LiNbO₃ layer 310 formed on the short-circuit electrode200, and (d) an interdigital transducer 400 formed on the LiNbO₃ layer310.

In the SAW device of the first embodiment, when the interdigitaltransducer 400 is used to excite an SAW, a plurality of SAWs withdifferent propagation velocities V are excited (0th-order mode,1st-order mode, 2nd-order mode, . . . in ascending order of thepropagation velocities V). Therefore, the mode of an SAW used in the SAWdevice can be determined by measuring the propagation velocity V of theSAW at the operating frequency of the device. This propagation velocityV can be obtained from, e.g., a relation V=fλ (f is the centerfrequency; λ is the wavelength based on the electrode width of theinterdigital transducer 400). When the interdigital transducer 400constituting the SAW device is a single electrode finger structure(electrode width d) having a planar shape as shown in FIG. 3, λ=4d. Whenthe interdigital transducer 400 is a double electrode finger structure(electrode width d) having a planar shape as shown in FIG. 4, λ=8d.

The SAW device of the first embodiment uses an SAW in the 1st-ordermode.

As the diamond 100, single crystal diamond and/or polycrystallinediamond can be used. The method of obtaining the diamond 100 is notparticularly limited. More specifically, single crystal diamond may beused as the diamond. In addition, a diamond layer may be formed on anymaterial (substrate) by epitaxial growth to obtain the diamond 100 as apolycrystalline diamond layer or an epitaxial diamond layer.

The base material for forming the diamond layer is not particularlylimited and can be appropriately selected depending on the applicationpurpose of the SAW device. In the first embodiment, a semiconductor suchas Si, a metal, a glass material, a ceramic, or the like can be used asthe material.

When the diamond 100 is a diamond layer, the method of growing thediamond layer is not particularly limited. More specifically, a knowntechnique such as CVD (Chemical Vapor Deposition), microwave plasma CVD,PVD (Physical Vapor Deposition), sputtering, ion plating, a plasma jetmethod, a flame method, or a hot filament method can be used as thegrowth method.

The plane orientation of the diamond 100 is not particularly limited.The diamond 100 can have a plane orientation (111), (100), or (110), orcan have two or more of them simultaneously.

When the diamond 100 is to be obtained as a layer, the thickness of thediamond 100 is set such that kh₂ ≧4 is satisfied when t₂ represents thethickness of the diamond 100, and a relation kh₂ =2π(t₂ /λ) holds.

If the diamond layer is thin, the SAW characteristics vary. However,when the thickness t₂ [μm] of the diamond layer is set such that kh₂ ≧4holds, the variation amount poses no practical problem. More preferably,kh₂ ≧8. In this case, the variation amount can be further reduced.

The short-circuit electrode 200 is an electrode having a function ofsetting an equipotential of an electric field to change the SAWcharacteristics of the device. The short-circuit electrode 200 ispreferably formed of a (thin) metal film (e.g., Al, Au, or Al--Cu).Since the short-circuit electrode 200 has a function different from thatof the interdigital transducer 400, the material of the short-circuitelectrode 200 need not be the same as that of the interdigitaltransducer 400.

The thickness of the short-circuit electrode 200 is not particularlylimited as far as the function as a short-circuit electrode can beobtained. However, it is preferably about 50 to 3,000 Å (morepreferably, about 100 to 500 Å). When this thickness is smaller than 50Å, it is difficult to set an equipotential. On the other hand, athickness larger than 3,000 Å results in a decrease in velocity of anSAW.

The short-circuit electrode 200 preferably has a planar shape of, e.g.,a "solid electrode" having the same area as that of the interdigitaltransducer 400.

The material of the interdigital transducer 400 is not particularlylimited as far as it is a conductive material. From the viewpoint ofworkability as an interdigital transducer and cost, Al (aluminum) can beparticularly preferably used.

The thickness of the interdigital transducer 400 is preferably about 100to 5,000 Å (more preferably, about 100 to 500 Å) though it is notparticularly limited as far as the function as an interdigitaltransducer can be obtained. When this thickness is smaller than 100 Å,the resistivity increases, resulting in an increase in loss. On theother hand, when the thickness of the electrode exceeds 5,000 Å, themass addition effect which causes reflection of an SAW due to thethickness and height of the electrode becomes conspicuous, and desiredSAW characteristics may be impeded.

The planar shape of the interdigital transducer 400 is not particularlylimited as far as the function as an interdigital transducer can beobtained. A so-called single electrode finger structure whose schematicplan view is shown in FIG. 3 or a double electrode finger structurewhose schematic plan view is shown in FIG. 4 can be preferably used.

The LiNbO₃ layer 310 is formed by bonding a cut single crystal LiNbO₃thin plate to the diamond 100 having the short-circuit electrode 200formed on its polished surface, and then polishing the single crystalLiNbO₃ thin plate.

For the LiNbO₃ layer 310, a thickness t₁ [μm] and a crystal orientation(θ[°],Φ[°],ψ[°]) are selected from the following values. Note that kh₁(=2π(t₁ /λ); λ=the wavelength [μm] of an SAW) is used instead of thethickness t₁.

An arbitrarily value within the range of 0°≦Φ≦30° is set. The remainingvalues are set on an orthogonal coordinate system (kh₁,θ,ψ).

(i) On the orthogonal coordinate system (kh₁,θ,ψ), values in theinternal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₁₁,B₁₁, C₁₁ and D₁₁, and a planar rectangular region with its vertexes atpoints A₁₂ B₁₂ C₁₂ and D₁₂,

where

point A₁₁ =(0.45, 80, 140)

point B₁₁ =(0.45, 100, 140)

point C₁₁ =(0.45, 100, 180)

point D₁₁ =(0.45, 80, 180)

point A₁₂ =(0.7, 70, 120)

point B₁₂ =(0.7, 110, 120)

point C₁₂ =(0.7, 110, 180)

point D₁₂ =(0.7, 60, 180).

(ii) On the orthogonal coordinate system (kh₁,θ, ψ), values in theinternal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₁₃B₁₃ C₁₃ and D₁₃, and a planar rectangular region with its vertexes atpoints A₁₄ B₁₄ C₁₄ and D₁₄,

where

point A₁₃ =(0.45, 80, 0)

point B₁₃ =(0.45, 90, 0)

point C₁₃ =(0.45, 90, 10)

point D₁₃ =(0.45, 80, 20)

point A₁₄ =(0.7, 60, 0)

point B₁₄ =(0.7, 110, 0)

point C₁₄ =(0.7, 90, 40)

point D₁₄ =(0.7, 80, 40).

In the structure of the SAW device according to the first embodiment,the propagation velocity V is exclusively determined by kh₁ of theLiNbO₃ layer 310. FIG. 5 is a graph showing the relationship between kh₁of the LiNbO₃ layer 310 and the propagation velocity V of an SAW in the1st-order mode in the SAW device of the first embodiment. It isconfirmed from FIG. 5 that, when kh₁ is equal to or smaller than 0.7, apropagation velocity V equal to or higher than 8,000 m/s is ensured.

The present inventors set the thickness of the diamond 100 at 20 μm, andevaluated an electromechanical coupling coefficient K² while changingkh₁ within the above-described limitation for kh₁ and simultaneouslychanging the values θ, Φ, and ψ.

FIGS. 6 to 21 are graphs showing contour lines obtained upon evaluatingthe electromechanical coupling coefficient K² [%] under conditions thatkh₁ =0.20, 0.325, 0.45, and 0.7, Φ=0°, 10°, 20°, and 30°, 0°≦θ≦180°, and0°≦ψ≦180°. Note that the values θ and ψ are plotted in units of 10° inthese graphs.

Regions for satisfying the electromechanical coupling coefficient K² of10% or more are obtained from FIGS. 6 to 21. Taking the symmetry of theLiNbO₃ crystal into consideration, it is confirmed that, when thepropagation velocity V is 8,000 m/s or more, and the electromechanicalcoupling coefficient K² is 10% or more, the value Φ is arbitrarily setwithin the range of 0°≦Φ≦360°, and the remaining parameters kh₁, θ, andψ are set, on the orthogonal coordinate system (kh₁,θ,ψ), in theinternal region of the symmetric hexahedron with that represented by (i)or (ii).

(Second Embodiment)

FIG. 22 is a sectional view showing the structure of an SAW deviceaccording to the second embodiment of the present invention. As shown inFIG. 22, the SAW device of the second embodiment is different from thatof the first embodiment only in that an SAW in the 2nd-order mode isused, and an LiNbO₃ layer 320 is formed in place of the LiNbO₃ layer310.

The LiNbO₃ layer 320 is formed by bonding a cut single crystal LiNbO₃thin plate to diamond 100 having a short-circuit electrode 200 formed onits polished surface, and then polishing the single crystal LiNbO₃ thinplate.

For the LiNbO₃ layer 320, a thickness t₁ [μm] and a crystal orientation(θ[°],Φ[°],ψ[°]) are selected from the following values. Note that kh₁(=2π(t₁ /λ); λ=the wavelength [μm] of an SAW) is used instead of thethickness t₁, as in the first embodiment.

(i) 0≦Φ≦15 on an orthogonal coordinate system (kh₁,θ,ψ), values in theinternal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₂₁B₂₁ C₂₁ and D₂₁, and a planar rectangular region with its vertexes atpoints A₂₂ B₂₂ C₂₂ and D₂₂,

where

point A₂₁ =(0.6, 60, 40)

point B₂₁ =(0.6, 110, 40)

point C₂₁ =(0.6, 110, 120)

point D₂₁ =(0.6, 60, 120)

point A₂₂ =(0.85, 50, 70)

point B₂₂ =(0.85, 130, 0)

point C₂₂ =(0.85, 130, 180)

point D₂₂ =(0.85, 50, 100).

(ii) 0≦Φ≦15 on the orthogonal coordinate system (kh₁,θ,ψ), values in theinternal regions of four hexahedrons each of which has, as its opposingbottom surfaces, the planar rectangular region with its vertexes at thepoints A₂₂ B₂₂ C₂₂ and D₂₂, and a planar rectangular region with itsvertexes at points A₂₃ B₂₃ C₂₃ and D₂₃,

where

point A₂₃ =(1.1, 40, 60)

point B₂₃ =(1.1, 140, 0)

point C₂₃ =(1.1, 140, 180)

point D₂₃ =(1.1, 40, 110).

(iii) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₂₄B₂₄ C₂₄ and D₂₄, and a planar rectangular region with its vertexes atpoints A₂₅ B₂₅ C₂₅ and D₂₅,

where

point A₂₄ =(0.6, 60, 30)

point B₂₄ =(0.6, 120, 30)

point C₂₄ =(0.6, 120, 100)

point D₂₄ =(0.6, 60, 100)

point A₂₅ =(0.85, 50, 30)

point B₂₅ =(0.85, 130, 30)

point C₂₅ =(0.85, 130, 110)

point D₂₅ =(0.85, 50, 110).

(iv) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, the planar rectangular region with its vertexes at the pointsA₂₅ B₂₅ C₂₅ and D₂₅, and a planar rectangular region with its vertexesat points A₂₆ B₂₆ C₂₆ and D₂₆.

where

point A₂₆ =(1.1, 40, 30)

point B₂₆ =(1.1, 140, 30)

point C₂₆ =(1.1, 140, 120)

point D₂₆ =(1.1, 40, 120).

In the structure of the SAW device according to the second embodiment, apropagation velocity V is exclusively determined by kh₁ of the LiNbO₃layer 320. FIG. 23 is a graph showing the relationship between kh₁ ofthe LiNbO₃ layer 320 and the propagation velocity V of an SAW in the2nd-order mode in the SAW device of the second embodiment. It isconfirmed from FIG. 23 that, when kh₁ is equal to or smaller than 1.1, apropagation velocity V equal to or higher than 8,000 m/s is ensured.

The present inventors set the thickness of the diamond 100 at 20 μm, andevaluated an electromechanical coupling coefficient K² while changingkh₁ within the above-described limitation for kh₁ and simultaneouslychanging the values θ, Φ, and ψ.

FIGS. 24 to 39 are graphs showing contour lines obtained upon evaluatingthe electromechanical coupling coefficient K² [%] under conditions thatkh₁ =0.6, 0.85, 1.1, and 1.6, Φ=0°, 10°, 20°, and 30°, 0°≦θ≦180°, and0°≦ψ≦180°. Note that the values θ and ψ are plotted in units of 10° inthese graphs.

Regions for satisfying the electromechanical coupling coefficient K² of10% or more are obtained from FIGS. 24 to 39. Taking the symmetry of theLiNbO₃ crystal into consideration, it is confirmed that, when thepropagation velocity V is 8,000 m/s or more, and the electromechanicalcoupling coefficient K² is 10% or more, the four parameters k₂, θ, Φ,and ψ are set in the internal region of one of the hexahedrons which aresymmetric with those represented by (i), (ii), (iii), or (iv).

(Third Embodiment)

FIG. 40 is a sectional view showing the structure of an SAW deviceaccording to the third embodiment of the present invention. As shown inFIG. 40, the SAW device of the third embodiment comprises (a) diamond100, (b) an interdigital transducer 400 formed on the diamond 100, (c) asingle crystal LiNbO₃ layer 330 formed on the interdigital transducer400, and (d) a short-circuit electrode 200 formed on the LiNbO₃ layer330.

The SAW device of the third embodiment uses an SAW in the 1st-ordermode.

The LiNbO₃ layer 330 is formed by bonding a cut single crystal LiNbO₃thin plate to the diamond 100 having the interdigital transducer 400formed on its polished surface, and then polishing the single crystalLiNbO₃ thin plate. For the interdigital transducer 400, preferably, arecessed portion is formed in the diamond 100 by reactive ion etching,the interdigital transducer 400 is formed with Al or the le in thisrecessed portion, and the interface to the LiNbO₃ layer 330 is entirelyflattened.

For the LiNbO₃ layer 330, a thickness t₁ [μm] and a crystal orientation(θ[°],Φ[°],ψ[°]) are selected from the following values. Note that kh₁(=2π(t₁ /λ); λ=the wavelength [μm] of an SAW) is used instead of thethickness t₁, as in the first embodiment.

(i) 0≦Φ≦15 on an orthogonal coordinate system (kh₁,θ,ψ), values in theinternal region of a quadrangular pyramid which has its vertex at apoint P₃₁ and, as its bottom surface, a planar rectangular region withits vertexes at points A₃₁ B₃₁ C₃₁ and D₃₁,

where

point P₃₁ =(0.45, 90, 150)

point A₃₁ =(0.7, 70, 130)

point B₃₁ =(0.7, 90, 130)

point C₃₁ =(0.7, 90, 180)

point D₃₁ =(0.7, 70, 180).

(ii) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal regions of four hexahedrons each of which has, as itsopposing bottom surfaces, a planar rectangular region with its vertexesat points A₃₂ B₃₂ C₃₂ and D₃₂ and a planar rectangular region with itsvertexes at points A₃₃ B₃₃ C₃₃ and D₃₃,

where

point A₃₂ =(0.45, 80, 130)

point B₃₂ =(0.45, 100, 130)

point C₃₂ =(0.45, 100, 150)

point D₃₂ =(0.45, 80, 150)

point A₃₃ =(0.7, 70, 120)

point B₃₃ =(0.7, 110, 120)

point C₃₃ =(0.7, 110, 160)

point D₃₃ =(0.7, 70, 160).

In the structure of the SAW device according to the third embodiment, apropagation velocity V is exclusively determined by kh₁ of the LiNbO₃layer 330, as in the first embodiment, as shown in FIG. 5. Therefore, asin the first embodiment, it is confirmed that, when kh₁ is equal to orsmaller than 1.1, a propagation velocity V equal to or higher than 8,000m/s is ensured.

The present inventors set the thickness of the diamond 100 at 20 μm, andevaluated an electromechanical coupling coefficient K² while changingkh₁ within the above-described limitation for kh₁ and simultaneouslychanging the values θ, Φ, and ψ.

FIGS. 41, to 56 are graphs showing contour lines obtained uponevaluating the electromechanical coupling coefficient K² [%] underconditions that kh₁ =0.2, 0.325, 0.45, and 0.7, Φ=0°, 10°, 20°, and 30°,0°≦θ≦180°, and 0°≦ψ≦180°. Note that the values θ and ψ are plotted inunits of 10° in these graphs.

Regions for satisfying the electromechanical coupling coefficient K² of10% or more are obtained from FIGS. 41 to 56. Taking the symmetry of theLiNbO₃ crystal into consideration, it is confirmed that, when thepropagation velocity V is 8,000 m/s or more, and the electromechanicalcoupling coefficient K² is 10% or more, the four parameters kh₁, θ, Φ,and ψ are set in the internal region of the symmetric quadrangularpyramid with that represented by (i) or the symmetric hexahedron withthat represented by (ii).

(Fourth Embodiment)

FIG. 57 is a sectional view showing the structure of an SAW deviceaccording to the fourth embodiment of the present invention. As shown inFIG. 57, the SAW device of the fourth embodiment is different from thatof the third embodiment only in that an SAW in the 2nd-order mode isused, and an LiNbO₃ layer 340 is formed in place of the LiNbO₃ layer330.

The LiNbO₃ layer 340 is formed by bonding a cut single crystal LiNbO₃thin plate to diamond 100 having a short-circuit electrode 200 formed onits polished surface, and then polishing the single crystal LiNbO₃ thinplate. As in the third embodiment, for an interdigital transducer 400,preferably, a recessed portion is formed in the diamond 100 by reactiveion etching, the interdigital transducer 400 is formed with Al or the lein this recessed portion, and the interface to the LiNbO₃ layer 340 isentirely flattened.

For the LiNbO₃ layer 340, a thickness t₁ [μm] and a crystal orientation(θ[°],Φ[°],ψ[°]) are selected from the following values. Note that kh₁(=2π(t₁ /λ); λ=the wavelength [μm] of an SAW) is used instead of thethickness t₁, as in the first embodiment.

(i) 0<Φ≦15 on an orthogonal coordinate system (kh₁,θ,ψ), values in theinternal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₄₁B₄₁ C₄₁ and D₄₁, and a planar rectangular region with its vertexes atpoints A₄₂ B₄₂ C₄₂ and D₄₂,

where

point A₄₁ =(0.6, 70, 40)

point B₄₁ =(0.6, 100, 40)

point C₄₁ =(0.6, 100, 110)

point D₄₁ =(0.6, 70, 110)

point A₄₂ =(0.85, 70, 60)

point B₄₂ =(0.85, 120, 0)

point C₄₂ =(0.85, 120, 180)

point D₄₂ =(0.85, 70, 100).

(ii) 0≦Φ≦15 on the orthogonal coordinate system (kh₁,θ,ψ), values in theinternal region of a hexahedron which has, as its opposing bottomsurfaces, the planar rectangular region with its vertexes at the pointsA₄₂ B₄₂ C₄₂ and D₄₂, and a planar rectangular region with its vertexesat points A₄₃ B₄₃ C₄₃ and D₄₃,

where

point A₄₃ =(1.1, 90, 0)

point B₄₃ =(1.1, 130, 0)

point C₄₃ =(1.1, 130, 180)

point D₄₃ =(1.1, 90, 180).

(iii) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₄₄B₄₄ C₄₄ and D₄₄, and a planar rectangular region with its vertexes atpoints A₄₅ B₄₅ C₄₅ and D₄₅,

where

point A₄₄ =(0.6, 70, 20)

point B₄₄ =(0.6, 110, 20)

point C₄₄ =(0.6, 100, 90)

point D₄₄ =(0.6, 70, 90)

point A₄₅ =(0.85, 60, 10)

point B₄₅ =(0.85, 120, 10)

point C₄₅ =(0.85, 120, 90)

point D₄₅ =(0.85, 60, 90).

(iv) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, the planar rectangular region with its vertexes at the pointsA₄₅ B₄₅ C₄₅ and D₄₅, and a planar rectangular region with its vertexesat points A₄₆ B₄₆ C₄₆ and D₄₆,

where

point A₄₆ =(1.1, 80, 10)

point B₄₆ =(1.1, 120, 10)

point C₄₆ =(1.1, 130, 80)

point D₄₆ =(1.1, 50, 80).

In the structure of the SAW device according to the fourth embodiment, apropagation velocity V is exclusively determined by kh₁ of the LiNbO₃layer 320. FIG. 23 is a graph showing the relationship between kh₁ ofthe LiNbO₃ layer 340 and the propagation velocity V of an SAW in the1st-order mode in the SAW device of the fourth embodiment. It isconfirmed from FIG. 23 that, when kh₁ is equal to or smaller than 1.1, apropagation velocity V equal to or higher than 8,000 m/s is ensured.

The present inventors set the thickness of the diamond 100 at 20 μm, andevaluated an electromechanical coupling coefficient K² while changingkh₁ within the above-described limitation for kh₁ and simultaneouslychanging the values θ, Φ, and ψ.

FIGS. 58 to 73 are graphs showing contour lines obtained upon evaluatingthe electromechanical coupling coefficient K² [%] under conditions thatkh₁ =0.6, 0.85, 1.1, and 1.6, Φ=0°, 10°, 20°, and 30°, 0°≦θ≦180°, and0°≦ψ≦180°. Note that the values θ and ψ are plotted in units of 10° inthese graphs.

Regions for satisfying the electromechanical coupling coefficient K² of10% or more are obtained from FIGS. 58 to 73. Taking the symmetry of theLiNbO₃ crystal into consideration, it is confirmed that, when thepropagation velocity V is 8,000 m/s or more, and the electromechanicalcoupling coefficient K² is 10% or more, the four parameters k₁, θ,Φ, andψ are set in the internal region of one of the hexahedrons which aresymmetric with those represented by (i), (ii), (iii), or (iv).

(Fifth Embodiment)

FIG. 74 is a sectional view showing the structure of an SAW deviceaccording to the fifth embodiment of the present invention. As shown inFIG. 74, the SAW device of the fifth embodiment comprises (a) diamond100, (b) a single crystal LiNbO₃ layer 350 formed on an interdigitaltransducer 400, and (c) the interdigital transducer 400 formed on thediamond 100.

The SAW device of the fifth embodiment uses an SAW in the 1st-ordermode.

The LiNbO₃ layer 350 is formed by bonding a cut single crystal LiNbO₃thin plate to the diamond 100 having the interdigital transducer 400formed on its polished surface, and then polishing the single crystalLiNbO₃ thin plate.

For the LiNbO₃ layer 350, a thickness t₁ [μm] and a crystal orientation(θ[°],Φ[°],ψ[°]) are selected from the following values. Note that kh₁(=2π(t₁ /λ); λ=the wavelength [μm] of an SAW) is used instead of thethickness t₁, as in the first embodiment.

(i) On an orthogonal coordinate system (kh₁,θ,ψ), values in the internalregion of a quadrangular pyramid which has its vertex at a point P₅₁and, as its bottom surface, a planar rectangular region with itsvertexes at points A₅₁ B₅₁ C₅₁ and D₅₁,

where

point P₅₁ =(0.6, 90, 0)

point A₅₁ =(0.7, 80, 0)

point B₅₁ =(0.7, 110, 0)

point C₅₁ =(0.7, 110, 10)

point D₅₁ =(0.7, 80, 10).

(ii) On the orthogonal coordinate system (kh₁,θ, ψ), values in theinternal region of a quadrangular pyramid which has its vertex at apoint P₅₂ and, as its bottom surface, a planar rectangular region withits vertexes at points A₅₂ B₅₂ C₅₂ and D₅₂,

where

point P₅₂ =(0.6, 100, 0)

point A₅₂ =(0.7, 90, 170)

point B₅₂ =(0.7, 100, 170)

point C₅₂ =(0.7, 110, 180)

point D₅₂ =(0.7, 80, 180).

In the structure of the SAW device according to the fifth embodiment, apropagation velocity V is exclusively determined by kh₁ of the LiNbO₃layer 350, as in the first embodiment, as shown in FIG. 5. Therefore, asin the first embodiment, it is confirmed that, when kh₁ is equal to orsmaller than 1.1, a propagation velocity V equal to or higher than 8,000m/s is ensured.

The present inventors set the thickness of the diamond 100 at 20 μm, andevaluated an electromechanical coupling coefficient K² while changingkh₁ within the above-described limitation for kh₁ and simultaneouslychanging the values θ, Φ, and ψ.

FIGS. 75 to 90 are graphs showing contour lines obtained upon evaluatingthe electromechanical coupling coefficient K² [%] under conditions thatkh₁ =0.2, 0.325, 0.45, and 0.7, Φ=0°, 10°, 20°, and 30°, 0°≦θ≦180°, and0°≦ψ≦180°. Note that the values θ and ψ are plotted in units of 100 inthese graphs.

Regions for satisfying the electromechanical coupling coefficient K² of10% or more are obtained from FIGS. 75 to 90. Taking the symmetry of theLiNbO₃ crystal into consideration, it is confirmed that, when thepropagation velocity V is 8,000 m/s or more, and the electromechanicalcoupling coefficient K² is 10% or more, the four parameters kh₁, θ, Φ,and ψ are set in the internal region of one of the quadrangular pyramidswhich are symmetric with those represented by (i), (ii), (iii), or (iv).

(Sixth Embodiment)

FIG. 91 is a sectional view showing the structure of an SAW deviceaccording to the sixth embodiment of the present invention. As shown inFIG. 91, the SAW device of the sixth embodiment is different from thatof the fifth embodiment only in that an SAW in the 2nd-order mode isused, and an LiNbO₃ layer 360 is formed in place of the LiNbO₃ layer350.

The LiNbO₃ layer 360 is formed by bonding a cut single crystal LiNbO₃thin plate to diamond 100 having a short-circuit electrode 200 formed onits polished surface, and then polishing the single crystal LiNbO₃ thinplate, as in the fifth embodiment.

For the LiNbO₃ layer 360, a thickness t₁ [μm] and a crystal orientation(θ[°],Φ[°],ψ[°]) are selected from the following values. Note that kh₁(=2π(t₁ /λ); λ=the wavelength [μm] of an SAW) is used instead of thethickness t₁, as in the first embodiment.

(i) 0≦Φ≦15 on an orthogonal coordinate system (kh₁,θ,ψ), values in theinternal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₆₁B₆₁ C₆₁ and D₆₁, and a planar rectangular region with its vertexes atpoints A₆₂ B₆₂ C₆₂ and D₆₂,

where

point A₆₁ =(0.85, 140, 40)

point B₆₁ =(0.85, 160, 40)

point C₆₁ =(0.85, 160, 60)

point D₆₁ =(0.85, 140, 60)

point A₆₂ =(1.1, 120, 30)

point B₆₂ =(1.1, 170, 30)

point C₆₂ =(1.1, 170, 70)

point D₆₂ =(1.1, 120, 70).

(ii) 0≦Φ≦15 on the orthogonal coordinate system (kh₁,θ,ψ), values in theinternal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₆₃B₆₃ C₆₃ and D₆₃, and a planar rectangular region with its vertexes atpoints A₆₄ B₆₄ C₆₄ and D₆₄,

where

point A₆₃ =(0.85, 130, 130)

point B₆₃ =(0.85, 160, 130)

point C₆₃ =(0.85, 160, 150)

point D₆₃ =(0.85, 130, 150)

point A₆₄ =(1.1, 100, 140)

point B₆₄ =(1.1, 140, 100)

point C₆₄ =(1.1, 160, 160)

point D₆₄ =(1.1, 130, 160).

(iii) 0≦Φ≦15 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a quadrangular pyramid which has its vertex at apoint P₆₅ and, as its bottom surface, a planar rectangular region withits vertexes at points A₆₅ B₆₅ C₆₅ and D₆₅,

where

point P₆₅ =(0.85,30,90)

point A₆₅ =(1.1,20,70)

point B₆₅ =(1.1,40,70)

point C₆₅ =(1.1,40,110)

point D₆₅ =(1.1,20,110).

(iv) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₆₆B₆₆ C₆₆ and D₆₆, and a planar rectangular region with its vertexes atpoints A₆₇ B₆₇ C₆₇ and D₆₇,

where

point A₆₆ =(0.6, 20, 150)

point B₆₆ =(0.6, 40, 150)

point C₆₆ =(0.6, 40, 170)

point D₆₆ =(0.6, 20, 170)

point A₆₇ =(0.85, 50, 130)

point B₆₇ =(0.85, 70, 140)

point C₆₇ =(0.85, 50, 160)

point D₆₇ =(0.85, 20, 160).

(v) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ, ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, the planar rectangular region with its vertexes at the pointsA₆₇ B₆₇ C₆₇ and D₆₇, and a planar rectangular region with its vertexesat points A₆₈ B₆₈ C₆₈ and D₆₈,

where

point A₆₈ =(1.1, 40, 120)

point B₆₈ =(1.1, 90, 120)

point C₆₈ =(1.1, 90, 160)

point D₆₈ =(1.1, 40, 160).

(vi) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₆₉B₆₉ C₆₉ and D₆₉, and a planar rectangular region with its vertexes atpoints A_(6A) B_(6A) C_(6A) and D_(6A),

where

point A₆₉ =(0.6, 140, 150)

point B₆₉ =(0.6, 160, 150)

point C₆₉ =(0.6, 160, 160)

point D₆₉ =(0.6, 140, 160)

point A_(6A) =(0.85, 100, 140)

point B_(6A) =(0.85, 130, 130)

point C_(6A) =(0.85, 160, 160)

point D_(6A) =(0.85, 130, 160).

(vii) 15≦≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, the planar rectangular region with its vertexes at the pointsA_(6A) B_(6A) C_(6A) and D_(6A), and a planar rectangular region withits vertexes at points A_(6B) B_(6B) C_(6B) and D_(6B),

where

point A_(6B) =(1.1, 100, 120)

point B_(6B) =(1.1, 150, 120)

point C_(6B) =(1.1, 150, 160)

point D_(6B) =(1.1, 100, 160).

(viii) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A_(6C)B_(6C) C_(6C) and D_(6C), and a planar rectangular region with itsvertexes at points A_(6D) B_(6D) C_(6D) and D_(6D),

where

point A_(6C) =(0.85, 150, 50)

point B_(6C) =(0.85, 160, 50)

point C_(6C) =(0.85, 160, 60)

point D_(6C) =(0.85, 150, 60)

point A_(6D) =(1.1, 130, 40)

point B_(6D) =(1.1, 160, 40)

point C_(6D) =(1.1, 160, 90)

point D_(6D) =(1.1, 130, 90).

(ix) 15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values inthe internal region of a quadrangular pyramid which has its vertex at apoint P_(6E) and, as its bottom surface, a planar rectangular regionwith its vertexes at points A_(6E) B_(6E) C_(6E) and D_(6E),

where

point P_(6E) =(0.85, 30, 70)

point A_(6E) =(1.1, 20, 50)

point B_(6E) =(1.1, 40, 50)

point C_(6E) =(1.1, 40, 90)

point D_(6E) =(1.1, 20, 90).

In the structure of the SAW device according to the sixth embodiment, apropagation velocity V is exclusively determined by kh₁ of the LiNbO₃layer 360, as in the second embodiment, as shown in FIG. 23. Therefore,it is confirmed that, when kh₁ is equal to or smaller than 1.1, apropagation velocity V equal to or higher than 8,000 m/s is ensured.

The present inventors set the thickness of the diamond 100 at 20 μm, andevaluated an electromechanical coupling coefficient K² while changingkh₁ within the above-described limitation for kh₁ and simultaneouslychanging the values θ, Φ, and ψ.

FIGS. 92 to 107 are graphs showing contour lines obtained uponevaluating the electromechanical coupling coefficient K² [%] underconditions that kh₁ =0.6, 0.85, 1.1, and 1.6, Φ=0°, 10°, 20°, and 30°,0°≦θ≦180°, and 0°≦ψ≦180°. Note that the values θ and ψ are plotted inunits of 10° in these graphs.

Regions for satisfying the electromechanical coupling coefficient K² of10% or more are obtained from FIGS. 92 to 107. Taking the symmetry ofthe LiNbO₃ crystal into consideration, it is confirmed that, when thepropagation velocity V is 8,000 m/s or more, and the electromechanicalcoupling coefficient K² is 10% or more, the four parameters kh₁, θ,Φ,and ψ are set in the internal region of one of the hexahedrons which aresymmetric with those represented by (i), (ii), (iv), (v), (vi), (vii),or (viii), or one of the quadrangular pyramids which are symmetric withthose represented by (iii) or (ix).

(Seventh Embodiment)

FIG. 108 is a sectional view showing the structure of an SAW deviceaccording to the seventh embodiment of the present invention. As shownin FIG. 108, the SAW device of the seventh embodiment comprises (a)diamond 100, (b) an interdigital transducer 400 formed on the diamond100, and (c) a single crystal LiNbO³ layer 370 formed on theinterdigital transducer 400.

The SAW device of the seventh embodiment uses an SAW in the 2nd-ordermode.

The LiNbO₃ layer 370 is formed by bonding a cut single crystal LiNbO₃thin plate to the diamond 100 having the interdigital transducer 400formed on its polished surface, and then polishing the single crystalLiNbO₃ thin plate. As in the third embodiment, for the interdigitaltransducer 400, preferably, a recessed portion is formed in the diamond100 by reactive ion etching, the interdigital transducer 400 is formedwith Al or the le in this recessed portion, and the interface to theLiNbO₃ layer 370 is entirely flattened.

For the LiNbO₃ layer 370, a thickness t₁ [μm] and a crystal orientation(θ[°], Φ[°], ψ[°]) are selected from the following values. Note that kh₁(=2π(t₁ /λ); λ=the wavelength [μm] of an SAW) is used instead of thethickness t₁, as in the first embodiment.

15≦Φ≦30 on an orthogonal coordinate system (kh₁,θ,ψ), values in theinternal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertexes at points A₇₁B₇₁ C₇₁ and D₇₁, and a planar rectangular region with its vertexes atpoints A₇₂ B₇₂ C₇₂ and D₇₂,

where

point A₇₁ =(0.85, 50, 160)

point B₇₁ =(0.85, 100, 160)

point C₇₁ =(0.85, 90, 170)

point D₇₁ =(0.85, 50, 170)

point A₇₂ =(1.1, 40, 150)

point B₇₂ =(1.1, 140, 150)

point C₇₂ =(1.1, 140, 180)

point D₇₂ =(1.1, 40, 180).

In the structure of the SAW device according to the seventh embodiment,a propagation velocity V is exclusively determined by kh₁ of the LiNbO₃layer 370, as in the second embodiment, as shown in FIG. 23. Therefore,it is confirmed that, when kh₁ is equal to or smaller than 1.1, apropagation velocity V equal to or higher than 8,000 m/s is ensured.

The present inventors set the thickness of the diamond 100 at 20 μm, andevaluated an electromechanical coupling coefficient K² while changingkh₁ within the above-described limitation for kh₁ and simultaneouslychanging the values θ, Φ, and ψ.

FIGS. 109 to 124 are graphs showing contour lines obtained uponevaluating the electromechanical coupling coefficient K² [%] underconditions that kh₁ =0.6, 0.85, 1.1, and 1.6, Φ=0°, 10°, 20°, and 30°,0°≦θ≦180°, and 0°≦ψ≦180°. Note that the values θ and ψ are plotted inunits of 10° in these graphs.

Regions for satisfying the electromechanical coupling coefficient K² of10% or more are obtained from FIGS. 109 to 124. Taking the symmetry ofthe LiNbO₃ crystal into consideration, it is confirmed that, when thepropagation velocity V is 8,000 m/s or more, and the electromechanicalcoupling coefficient K² is 10% or more, the four parameters kh₁, θ, Φ,and ψ are set in the internal region of the hexahedron which issymmetric with the above hexahedron.

The present inventors evaluated an electromechanical couplingcoefficient K² of an SAW device having the same structure as in theseventh embodiment and using the 1st-order mode while changing kh₁ andsimultaneously changing the values θ, Φ, and ψ.

FIGS. 125 to 140 are graphs showing contour lines obtained uponevaluating the electromechanical coupling coefficient K² [%] underconditions that kh₁ =0.2, 0.325, 0.6, and 0.7, Φ=0°, 10°, 20°, and 30°,0°≦θ≦180°, and 0°≦ψ≦180°. Note that the values θ and ψ are plotted inunits of 10° in these graphs.

It is confirmed from FIGS. 125 to 140 that no region for satisfying theelectromechanical coefficient K² ≧10% is present.

In the above description and the claims, the embodiement are determinedwithin 0°≦Φ≦30°, 0°θ≦180°, and 0°≦ψ≦180°. Because of the symmetry of theLiNbO₃ crystall, it is obvious that there are many examples equivalentto those embodiements. For example, on the coordinate system (θ, Φ, ψ),the value (a, b, c) from 0≦a≦180, 0≦b≦30°, and 0≦c≦180 is one of theabove embodiements, the values (a+180i, b+120j, c+180k), (180(1+i)-a,60-b+120j, c+180k), (180(1+i)-a, b+60+120j, 180(1+k)-c) and (a+180i,120-b+120j, 180(1+k)-c), wherein i=0 or 1, j=0, 1 or 2, k=0 or 1, areequivalent to the above embodiements and they also involved in thepresent invention.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

The basic Japanese Application No. 8-155024 (155024/1996) filed on Feb.9, 1996 is hereby incorporated by reference.

What is claimed is:
 1. A surface acoustic wave devicecomprising:diamond; a single crystal LiNbO₃ layer formed on a surface ofsaid diamond; and an interdigital transducer formed on one of a surfaceof said LiNbO₃ layer and an interface between said diamond and saidLiNbO₃ layer, wherein a crystal orientation of said LiNbO₃ layer withrespect to an exposed surface of said LiNbO₃ layer and a propagationdirection of a surface acoustic wave, and a ratio of a thickness of saidLiNbO₃ layer to a wavelength of the surface acoustic wave to be used areselected such that a velocity of the surface acoustic wave to be usedbecomes 8,000 m/s and an electromechanical coupling coefficient becomesnot less than 10%; and wherein said device comprises said diamond, ashort-circuit electrode formed on said diamond, said single crystalLiNbO₃ layer formed on said short-circuit electrode, and saidinterdigital transducer formed on said LiNbO₃ layer, and uses a surfaceacoustic wave (wavelength: λ[μm]) in the 1^(st) -order mode, when anEulerian angle representation on an orthogonal coordinate system (X,Y,Z)in which a Z-axis is set along a normal direction of said exposedsurface of said LiNbO₃ layer, and an X-axis is set along the propagationdirection of the surface acoustic wave is represented by (θ[°], Φ[°],ψ[°]) with respect to a crystallographic fundamental coordinate system(x,y,z) of said LiNbO₃ layer, the thickness of said LiNbO₃ layer is t₁[μm], and kh₁ =2π(t₁ /λ), the values kh₁, θ, and ψ are selected from, onan orthogonal coordinate system (kh₁ θ, ψ), values in internal region ofa hexahedron which has, as its opposing bottom surfaces, a planarrectangular region with its vertices at points A₁₁ B₁₁ C₁₁ and D₁₁, anda planar rectangular region with its vertices at points A₁₂ B₁₂ C₁₂ andD₁₂, wherepoint A₁₁ =(0.45,80,140) point B₁₁ =(0.45,100,140) point C₁₁=(0.45,100,180) point D₁₁ =(0.45,80,180) point A₁₂ =(0.7,70,120) pointB₁₂ =(0.7,110,120) point C₁₂ =(0.7,110,180) point D₁₂ =(0.7,60,180), andon the orthogonal coordinate system (kh₁ θ, ψ), values in internalregion of a hexahedron which has, as its opposing bottom surfaces, aplanar rectangular region with its vertices at points A₁₃ B₁₃ C₁₃ andD₁₃, and a planar rectangular region with its vertices at points A₁₄ B₁₄C₁₄ and D₁₄, wherepoint A₁₃ =(0.45,80,0) point B₁₃ =(0.45,90,0) pointC₁₃ =(0.45,90,10) point D₁₃ =(0.45,80,20) point A₁₄ =(0.7,60,0) pointB₁₄ =(0.7,110,0) point C₁₄ =(0.7,90,40) point D₁₄ =(0.7,80,40).
 2. Adevice according to claim 1, wherein said diamond is a diamond layerformed on a base material, and when a thickness of said diamond layer ist₂ [μm], and kh₂ =2π(t₂ /λ), the following relation is satisfied:kh₂ ≧4.3. A surface acoustic wave device comprising:diamond; a single crystalLiNbO₃ layer formed on a surface of said diamond; and an interdigitaltransducer formed on one of a surface of said LiNbO₃ layer and aninterface between said diamond and said LiNbO₃ layer, wherein a crystalorientation of said LiNbO₃ layer with respect to an exposed surface ofsaid LiNbO₃ layer and a propagation direction of a surface acousticwave, and a ratio of a thickness of said LiNbO₃ layer to a wavelength ofthe surface acoustic wave to be used are selected such that a velocityof the surface acoustic wave to be used becomes 8,000 m/s and anelectromechanical coupling coefficient becomes not less than 10%; andwherein said device comprises said diamond, a short-circuit electrodeformed on said diamond, said single crystal LiNbO₃ layer formed on saidshort-circuit electrode, and said interdigital transducer formed on saidLiNbO₃ layer, and uses a surface acoustic wave (wavelength: λ[μm]) inthe 2nd-order mode, when an Eulerian angle representation on anorthogonal coordinate system (X,Y,Z) in which a Z-axis is set along anormal direction of said exposed surface of said LiNbO₃ layer, and anX-axis is set along the propagation direction of the surface acousticwave is represented by (θ[°], Φ[°], ψ[°]) with respect to acrystallographic fundamental coordinate system (x,y,z) of said LiNbO₃layer, the thickness of said LiNbO₃ layer is t₁ [μm], and kh₁ =2π(t₁/λ), the values kh₁, θ, and ψ are selected from, 0≦Φ≦15 on an orthogonalcoordinate system (kh₁ θ, ψ), values in internal region of a hexahedronwhich has, as its opposing bottom surfaces, a planar rectangular regionwith its vertices at points A₂₁ B₂₁ C₂₁ and D₂₁, and a planarrectangular region with its vertices at points A₂₂ B₂₂ C₂₂ and D₂₂,wherepoint A₂₁ =(0.6,60,40) point B₂₁ =(0.6,110,40) point C₂₁=(0.6,110,120) point D₂₁ =(0.6,60,120) point A₂₂ =(0.85,50,70) point B₂₂=(0.85,130,0) point C₂₂ =(0.85,130,180) point D₂₂ =(0.85,50,100), 0≦Φ≦15on the orthogonal coordinate system (kh₁ θ, ψ), values in internalregion of a hexahedron which has, as its opposing bottom surfaces, theplanar rectangular region with its vertices at the points A₂₂ B₂₂ C₂₂and D₂₂, and a planar rectangular region with its vertices at points A₂₃B₂₃ C₂₃ and D₂₃, wherepoint A₂₆ =(1.1,40,60) point B₂₃ =(1.1,140,0)point C₂₃ =(1.1,140,180) point D₂₃ =(1.1,40,110), 15≦Φ≦30 on theorthogonal coordinate system (kh₁ θ, ψ), values in internal region of ahexahedron which has, as its opposing bottom surfaces, a planarrectangular region with its vertices at points A₂₄ B₂₄ C₂₄ and D₂₄, anda planar rectangular region with its vertices at points A₂₅ B₂₅ C₂₅ andD₂₅, wherepoint A₂₄ =(0.6,60,30) point B₂₄ =(0.6,120,30) point C₂₄=(0.6,120,100) point D₂₄ =(0.6,60,100) point A₂₅ =(0.85,50,30) point B₂₅=(0.85,130,30) point C₂₅ =(0.85,130,110) point D₂₅ =(0.85,50,110), and15≦Φ≦30 on the orthogonal coordinate system (kh₁ θ, ψ), values ininternal region of a hexahedron which has, as its opposing bottomsurfaces, the planar rectangular region with its vertices at the pointsA₂₅ B₂₅ C₂₅ and D₂₅, and a planar rectangular region with its verticesat points A₂₆ B₂₆ C₂₆ and D₂₆, wherepoint A₂₆ =(1.1,40,30) point B₂₆=(1.1,140,30) point C₂₆ =(1.1,140,120) point D₂₆ =(1.1,40,120).
 4. Adevice according to claim 3, wherein said diamond is a diamond layerformed on a base material, and when a thickness of said diamond layer ist₂ [μm], and kh₂ =2π(t₂ /λ), the following relation is satisfied:kh₂ ≧4.5. A surface acoustic wave device comprising:diamond; a single crystalLiNbO₃ layer formed on a surface of said diamond; and an interdigitaltransducer formed on one of a surface of said LiNbO₃ layer and aninterface between said diamond and said LiNbO₃ layer, wherein a crystalorientation of said LiNbO₃ layer with respect to an exposed surface ofsaid LiNbO₃ layer and a propagation direction of a surface acousticwave, and a ratio of a thickness of said LiNbO₃ layer to a wavelength ofthe surface acoustic wave to be used are selected such that a velocityof the surface acoustic wave to be used becomes 8,000 m/s and anelectromechanical coupling coefficient becomes not less than 10%; andwherein said device comprises said diamond, said interdigital transducerformed on said diamond, said single crystal LiNbO₃ layer formed on saidInterdigital transducer, and a short-circuit electrode formed on saidLiNbO₃ layer, and uses a surface acoustic wave (wavelength: λ[μm]) inthe 1st-order mode, when an Eulerian angle representation on anorthogonal coordinate system (X,Y,Z) in which a Z-axis is set along anormal direction of said exposed surface of said LiNbO₃ layer, and anX-axis is set along the propagation direction of the surface acousticwave is represented by (θ[°], Φ[°], ψ[°]) with respect to acrystallographic fundamental coordinate system (x,y,z) of said LiNbO₃layer, the thickness of said LiNbO₃ layer is t₁ [μm], and kh₁ =2π(t₁/λ), the values kh₁, θ, and ψ are selected from, 0≦Φ≦15 on an orthogonalcoordinate system (kh₁ θ, ψ), values in internal region of aquadrangular pyramid which has its vertex at a point P₃₁ and, as itsbottom surface, a planar rectangular region with its vertices at pointsA₃₁ B₃₁ C₃₁ and D₃₁, wherepoint P₃₁ =(0.45,90,150) point A₃₁=(0.7,70,130) point B₃₁ =(0.7,90,130) point C₃₁ =(0.7,90,180) point D₃₁=(0.7,70,180), and 15≦Φ≦30 on an orthogonal coordinate system (kh₁ θ,ψ), values in internal region of a hexahedron which has, as its opposingbottom surfaces, a planar rectangular region with its vertices at pointsA₃₂ B₃₂ C₃₂ and D₃₂, and a planar rectangular region with its verticesat points A₃₃ B₃₃ C₃₃ and D₃₃, wherepoint A₃₂ =(0.45,80,130) point B₃₂=(0.45,100,130) point C₃₂ =(0.45,100,150) point D₃₂ =(0.45,80,150) pointA₃₃ =(0.7,70,120) point B₃₃ =(0.7,110,120) point C₃₃ =(0.7,110,160)point D₃₃ =(0.7,70,160).
 6. A device according to claim 5, wherein saiddiamond is a diamond layer formed on a base material, and when athickness of said diamond layer is t₂ [μm], and kh₂ =2π(t₂ /λ), thefollowing relation is satisfied:kh₂ ≧4.
 7. A surface acoustic wavedevice comprising:diamond; a single crystal LiNbO₃ layer formed on asurface of said diamond; and an interdigital transducer formed on one ofa surface of said LiNbO₃ layer and an interface between said diamond andsaid LiNbO₃ layer, wherein a crystal orientation of said LiNbO₃ layerwith respect to an exposed surface of said LiNbO₃ layer and apropagation direction of a surface acoustic wave, and a ratio of athickness of said LiNbO₃ layer to a wavelength of the surface acousticwave to be used are selected such that a velocity of the surfaceacoustic wave to be used becomes 8,000 m/s and an electromechanicalcoupling coefficient becomes not less than 10%; and wherein said devicecomprises said diamond, said interdigital transducer formed on saiddiamond, said single crystal LiNbO₃ layer formed on said interdigitaltransducer, and a short-circuit electrode formed on said LiNbO₃ layer,and uses a surface acoustic wave (wavelength: λ[μm]) in the 2^(nd)-order mode, when an Eulerian angle representation on an orthogonalcoordinate system (X,Y,Z) in which a Z-axis is set along a normaldirection of said exposed surface of said LiNbO₃ layer, and an X-axis isset along the propagation direction of the surface acoustic wave isrepresented by (θ[°], Φ[°], ψ[°]) with respect to a crystallographicfundamental coordinate system (x,y,z) of said LiNbO₃ layer, thethickness of said LiNbO₃ layer is t₁ [μm], and kh₁ =2π(t₁ /λ), thevalues kh₁, θ, and ψ are selected from, 0≦Φ≦15 on an orthogonalcoordinate system (kh₁,θ,ψ), values in internal regions of a hexahedronwhich has, as its opposing bottom surfaces, a planar rectangular regionwith its vertices at points A₄₁ B₄₁ C₄₁ and D₄₁, and a planarrectangular region with its vertices at points A₄₂ B₄₂ C₄₂ and D₄₂,wherepoint A₄₁ =(0.6,70,40) point B₄₁ =(0.6,100,40) point C₄₁=(0.6,100,110) point D₄₁ =(0.6,70,110) point A₄₂ =(0.85,70,60) point B₄₂=(0.85,120,0) point C₄₂ =(0.85,120,180) point D₄₂ =(0.85,70,100), 0≦Φ≦15on the orthogonal coordinate system (kh₁,θ,ψ), values in internal regionof a hexahedrons which has, as its opposing bottom surfaces, the planarrectangular region with its vertices at the points A₄₂ B₄₂ C₄₂ and D₄₂,and a planar rectangular region with its vertices at points A₄₃ B₄₃ C₄₃and D₄₃, wherepoint A₄₃ =(1.1,90,0) point B₄₃ =(1.1,130,0) point C₄₃=(1.1,130,180) point D₄₃ =(1.1,90,180), 15≦Φ≦30 on the orthogonalcoordinate system (kh₁,θ,ψ), values in internal region of a hexahedronwhich has, as its opposing bottom surfaces, a planar rectangular regionwith its vertices at points A₄₄ B₄₄ C₄₄ and D₄₄, and a planarrectangular region with its vertices at points A₄₅ B₄₅ C₄₅ and D₄₅,wherepoint A₄₄ =(0.6,70,20) point B₄₄ =(0.6,110,20) point C₄₄=(0.6,100,90) point D₄₄ =(0.6,70,90) point A₄₅ =(0.85,60,10) point B₄₅=(0.85,120,10) point C₄₅ =(0.85,120,90) point D₄₅ =(0.85,60,90), and15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values ininternal region of a hexahedron which has, as its opposing bottomsurfaces, the planar rectangular region with its vertices at the pointsA₄₅ B₄₅ C₄₅ and D₄₅, and a planar rectangular region with its verticesat points A₄₆ B₄₆ C₄₆ and D₄₆, wherepoint A₄₆ =(1.1,80,10) point B₄₆=(1.1,120,10) point C₄₆ =(1.1,130,80) point D₄₆ =(1.1,50,80).
 8. Adevice according to claim 7, wherein said diamond is a diamond layerformed on a base material, and when a thickness of said diamond layer ist₂ [μm], and kh₂ =2π(t₂ /λ), the following relation is satisfied:kh₂ ≧4.9. A surface acoustic wave device comprising;diamond; a single crystalLiNbO₃ layer formed on a surface of said diamond; and an interdigitaltransducer formed on one of a surface of said LiNbO₃ layer and aninterface between said diamond and said LiNbO₃ layer, wherein a crystalorientation of said LiNbO₃ layer with respect to an exposed surface ofsaid LiNbO₃ layer and a propagation direction of a surface acousticwave, and a ratio of a thickness of said LiNbO₃ layer to a wavelength ofthe surface acoustic wave to be used are selected such that a velocityof the surface acoustic wave to be used becomes 8,000 m/s and anelectromechanical coupling coefficient becomes not less than 10%; andwherein said device comprises said diamond, said single crystal LiNbO₃layer formed on said diamond, and said interdigital transducer formed onsaid LiNbO₃ layer, and uses a surface acoustic wave (wavelength: λ[μm])in the 1^(st) -order mode, when an Eulerian angle representation on anorthogonal coordinate system (X,Y,Z) in which a Z-axis is set along anormal direction of said exposed surface of said LiNbO₃ layer, and anX-axis is set along the propagation direction of the surface acousticwave is represented by (θ[°], Φ[°], ψ[°]) with respect to acrystallographic fundamental coordinate system (x,y,z) of said LiNbO₃layer, the thickness of said LiNbO₃ layer is t₁ [μm], and kh₁ =2π(t₁/λ), the values kh₁, θ, and ψ are selected from, on an orthogonalcoordinate system (kh₁,θ,ψ), values in internal region of a quadrangularpyramid which has its vertex at a point P₅₁ and, as its bottom surface,a planar rectangular region with its vertices at points A₅₁ B₅₁ C₅₁ andD₅₁, wherepoint P₅₁ =(0.6,90,0) point A₅₁ =(0.7,80,0) point B₅₁=(0.7,110,0) point C₅₁ =(0.7,110,10) point D₅₁ =(0.7,80,10), and on theorthogonal coordinate system (kh₁,θ,ψ), values in internal region of aquadrangular pyramid which has its vertex at a point P₅₂ and, as itsbottom surface, a planar rectangular region with its vertices at pointsA₅₂ B₅₂ C₅₂ and D₅₂, wherepoint P₅₂ =(0.6,100,0) point A₅₂ =(0.7,90,170)point B₅₂ =(0.7,100,170) point C₅₂ =(0.7,110,180) point D₅₂=(0.7,80,180).
 10. A device according to claim 9, wherein said diamondis a diamond layer formed on a base material, and when a thickness ofsaid diamond layer is t₂ [μm], and kh₂ =2π(t₂ /λ), the followingrelation is satisfied:kh₂ ≧4.
 11. A surface acoustic wave devicecomprising:diamond; a single crystal LiNbO₃ layer formed on a surface ofsaid diamond; and an interdigital transducer formed on one of a surfaceof said LiNbO₃ layer and an interface between said diamond and saidLiNbO₃ layer, wherein a crystal orientation of said LiNbO₃ layer withrespect to an exposed surface of said LiNbO₃ layer and a propagationdirection of a surface acoustic wave, and a ratio of a thickness of saidLiNbO₃ layer to a wavelength of the surface acoustic wave to be used areselected such that a velocity of the surface acoustic wave to be usedbecomes 8,000 m/s and an electromechanical coupling coefficient becomesnot less than 10%; and wherein said device comprises said diamond, saidsingle crystal LiNbO₃ layer formed on said diamond, and saidinterdigital transducer formed on said LiNbO₃ layer, and uses a surfaceacoustic wave (wavelength: λ[μm]) in the 2^(nd) -order mode, when anEulerian angle representation on an orthogonal coordinate system (X,Y,Z)in which a Z-axis is set along a normal direction of said exposedsurface of said LiNbO₃ layer, and an X-axis is set along the propagationdirection of the surface acoustic wave is represented by (θ[°], Φ[°],ψ[°]) with respect to a crystallographic fundamental coordinate system(x,y,z) of said LiNbO₃ layer, the thickness of said LiNbO₃ layer is t₁[μm], and kh₁ =2π(t₁ /λ), the values kh₁, θ, and ψ are selected from,0≦Φ≦15 on an orthogonal coordinate system (kh₁,θ,ψ), values in internalregion of a hexahedron which has, as its opposing bottom surfaces, aplanar rectangular region with its vertices at points A₆₁ B₆₁ C₆₁ andD₆₁, and a planar rectangular region with its vertices at points A₆₂ B₆₂C₆₂ and D₆₂, wherepoint A₆₁ =(0.85,140,40) point B₆₁ =(0.85,160,40)point C₆₁ =(0.85,160,60) point D₆₁ =(0.85,140,60) point A₆₂=(1.1,120,30) point B₆₂ =(1.1,170,30) point C₆₂ =(1.1,170,70) point D₆₂=(1.1,120,70), 0≦Φ≦15 on the orthogonal coordinate system (kh₁,θ,ψ),values in internal region of a hexahedron which has, as its opposingbottom surfaces, a planar rectangular region with its vertices at pointsA₆₃ B₆₃ C₆₃ and D₆₃, and a planar rectangular region with its verticesat points A₆₄ B₆₄ C₆₄ and D₆₄, wherepoint A₆₃ =(0.85,130,130) point B₆₃=(0.85,160,130) point C₆₃ =(0.85,160,150) point D₆₃ =(0.85,130,150)point A₆₄ =(1.1,100,140) point B₆₄ =(1.1,140,100) point C₆₄=(1.1,160,160) point D₆₄ =(1.1,130,160), 0≦Φ≦15 on the orthogonalcoordinate system (kh₁ θ,ψ), values in internal region of a quadrangularpyramid which has its vertex at a point P₆₅ and, as its bottom surface,a planar rectangular region with its vertices at points A₆₅ B₆₅ C₆₅ andD₆₅, wherepoint P₆₅ =(0.85,30,90) point A₆₅ =(1.1,20,70) point B₆₅=(1.1,40,70) point C₆₅ =(1.1,40,110) point D₆₅ =(1.1,20,110), 15≦Φ≦30 onthe orthogonal coordinate system (kh₁,θ,ψ), values in internal region ofa hexahedron which has, as its opposing bottom surfaces, a planarrectangular region with its vertices at points A₆₆ B₆₆ C₆₆ and D₆₆, anda planar rectangular region with its vertices at points A₆₇ B₆₇ C₆₇ andD₆₇, wherepoint A₆₆ =(0.6,20,150) point B₆₆ =(0.6,40,150) point C₆₆=(0.6,40,170) point D₆₆ =(0.6,20,170) point A₆₇ =(0.85,50,130) point B₆₇=(0.85,70,140) point C₆₇ =(0.85,50,160) point D₆₇ =(0.85,20,160),15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values ininternal region of a hexahedron which has, as its opposing bottomsurfaces, the planar rectangular region with its vertices at the pointsA₆₇ B₆₇ C₆₇ and D₆₇, and a planar rectangular region with its verticesat points A₆₈ B₆₈ C₆₈ and D₆₈, wherepoint A₆₈ =(1.1,40,120) point B₆₈=(1.1,90,120) point C₆₈ =(1.1,90,160) point D₆₈ =(1.1,40,160), 15≦Φ≦30on the orthogonal coordinate system (kh₁,θ,ψ), values in internal regionof a hexahedron which has, as its opposing bottom surfaces, a planarrectangular region with its vertices at points A₆₉ B₆₉ C₆₉ and D₆₉, anda planar rectangular region with its vertices at points A_(6A) B_(6A)C_(6A) and D_(6A), wherepoint A₆₉ =(0.6,140,150) point B₆₉=(0.6,160,150) point C₆₉ =(0.6,160,160) point D₆₉ =(0.6,140,160) pointA_(6A) =(0.85,100,140) point B_(6A) =(0.85,130,130) point C_(6A)=(0.85,160,160) point D_(6A) =(0.85,130,160), 15≦Φ≦30 on the orthogonalcoordinate system (kh₁,θ,ψ), values in internal region of a hexahedronwhich has, as its opposing bottom surfaces, the planar rectangularregion with its vertices at the points A_(6A) B_(6A) C_(6A) and D_(6A),and a planar rectangular region with its vertices at points A_(6B)B_(6B) C_(6B) and D_(6B), wherepoint A_(6B) =(1.1,100,120) point B_(6B)=(1.1,150,120) point C_(6B) =(1.1,150,160) point D_(6B) =(1.1,100,160),15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values ininternal region of a hexahedron which has, as its opposing bottomsurfaces, a planar rectangular region with its vertices at points A_(6C)B_(6C) C_(6C) and D_(6C), and a planar rectangular region with itsvertices at points A_(6D) B_(6D) C_(6D) and D_(6D), wherepoint A_(6C)=(0.85,150,50) point B_(6C) =(0.85,160,50) point C_(6C) =(0.85,160,60)point D_(6C) =(0.85,150,60) point A_(6D) =(1.1,130,40) point B_(6D)=(1.1,160,40) point C_(6D) =(1.1,160,90) point D₆ D=(1.1,130,90), and15≦Φ≦30 on the orthogonal coordinate system (kh₁,θ,ψ), values ininternal region of a quadrangular pyramid which has its vertex at apoint P_(6E) and, as its bottom surface, a planar rectangular regionwith its vertices at points A_(6E) B_(6E) C_(6E) and D_(6E), wherepointP_(6E) =(0.85,30,70) point A_(6E) =(1.1,20,50) point B_(6E) =(1.1,40,50)point C_(6E) =(1.1,40,90) point D_(6E) =(1.1,20,90).
 12. A deviceaccording to claim 11, wherein said diamond is a diamond layer formed ona base material, and when a thickness of said diamond layer is t₂ [μm],and kh₂ =2π(t₂ /λ), the following relation is satisfied:kh₂ ≧4.
 13. Asurface acoustic wave device comprising:diamond; a single crystal LiNbO₃layer formed on a surface of said diamond; and an interdigitaltransducer formed on one of a surface of said LiNbO₃ layer and aninterface between said diamond and said LiNbO₃ layer, wherein a crystalorientation of said LiNbO₃ layer with respect to an exposed surface ofsaid LiNbO₃ layer and a propagation direction of a surface acousticwave, and a ratio of a thickness of said LiNbO₃ layer to a wavelength ofthe surface acoustic wave to be used are selected such that a velocityof the surface acoustic wave to be used becomes 8,000 m/s and anelectromechanical coupling coefficient becomes not less than 10%; andwherein said device comprises said diamond, said interdigital transducerformed on said diamond, and said single crystal LiNbO₃ layer formed onsaid interdigital transducer, and uses a surface acoustic wave(wavelength: λ[μm]) in the 2^(nd) -order mode, when an Eulerian anglerepresentation on an orthogonal coordinate system (X,Y,Z) in which aZ-axis is set along a normal direction of said exposed surface of saidLiNbO₃ layer, and an X-axis is set along the propagation direction ofthe surface acoustic wave is represented by (θ[°], Φ[°], ψ[°]) withrespect to a crystallographic fundamental coordinate system (x,y,z) ofsaid LiNbO₃ layer, the thickness of said LiNbO₃ layer is t₁ [μm], andkh₁ =2π(t₁ /λ), the values kh₁, ψ, and θ are selected from, 15≦Φ≦30 onan orthogonal coordinate system (k₁,θ,ψ), values in internal region of ahexahedron which has, as its opposing bottom surfaces, a planarrectangular region with its vertices at points A₇₁ B₇₁ C₇₁ and D₇₁, anda planar rectangular region with its vertices at points A₇₂ B₇₂ C₇₂ andD₇₂, wherepoint A₇₁ =(0.85,50,160) point B₇₁ =(0.85,100,160) point C₇₁=(0.85,90,170) point D₇₁ =(0.85,50,170) point A₇₂ =(1.1,40,150) pointB₇₂ =(1.1,140,150) point C₇₂ =(1.1,140,180) point D₇₂ =(1.1,40,180). 14.A device according to claim 13, wherein said diamond is a diamond layerformed on a base material, and when a thickness of said diamond layer ist₂ [μm], and kh₂ =2π(t₂ /λ), the following relation is satisfied:kh₂ ≧4.